The invention relates to a heat exchanging or accumulator structure made of plastic for the transfer of heat between gas streams, especially for reheating the boiler exhaust gases cleaned in a scrubber, but the transfer of heat from the foul boiler exhaust exhaust gases being delivered to the scubber.
Metal and ceramic substances are used as materials in regenerative heat exchangers for boiler and air conditioning plants, and for mobile and stationary gas turbines. An old proposal is known for selecting nonmetallic substances of poor thermal conductivity, such as plastics, asbestos, paper or textiles, in the low temperature range, depending on the working temperature in the particular application, for use principally in air-conditioning plants for heat exchange between fresh air and exhaust air (Swiss Pat. No. 334,078). Paper and textiles have not been successfully used, despite the use of selected impregnants and textile dressings, on account of their low wet strength, low stability of shape, high flammability and poor resistance to chemicals such as mineral or organic acids. Furthermore, in connection with the use of these materials in ventilation and airconditioning plants, there are considerable objections to paper and textiles on account of the danger of rotting.
Although plastics have been repeatedly mentioned as exchange materials, no experience has been had in such technical use of plastics. The thermal insulating properties peculiar, as a rule, to plastics, and poor resistance to breakdown under long-term exposure to high temperatures, militate against such use of plastics. Alternating stresses on plastics cause them to lose their stability rapidly with the passage of time.
The heat exchanging material used in the cores of regenerative heat exchangers for reheating previously scrubbed boiler exhaust gases by the transfer of heat from the foul boiler exhaust gases entering the scubber is subjected to special operational stresses. On the side absorbing the heat the material is in contact with raw gases of elevated temperature from which the dust has been removed incompletely or not at all, and on the heat-yielding side it is exposed to gases of low temperature and high moisture content which are carrying along with them residues of chemical sorption and neutralization agents and products from the wet scrubbing. Depending on the chemical composition of the precipitates formed within the accumulator material by the heat exchange under these conditions, the precipitates harden sooner or later to form crusts which adhere more or less tightly to the heat exchanging body and are as a rule insoluble in water, and which completely clog the passages in the core, so that continued operation of the heat exchanger and consequently of the boiler plant is impossible. To clean heavily contaminated and encrusted heating surfaces--usually made of steel or enameled steelW---of heat exchangers connected to the exhaust of boiler plants, soot blowers of special design have been used, whose cleaning jets clean the exchanger core in place, reopen the passages and reliably and completely blast the solid coatings out of the heat exchanging material of the heat exchanger. The powerful jets emerging from the nozzles of the soot blowers cause a fluttering of the plate-like components of the heat exchanging body. On the other hand, it is precisely such fluttering of the heat exchanging body that is in plate form that is especially capable of breaking off crusts and coatings that are tightly adhering to it.
Regenerative heat exchangers having metal cores, however, can be used under the special operating conditions described above only for limited periods of time and only with very greatly increased cleaning cost and difficulty.
The invention is therefore addressed to the problem of developing a heat exchanging body which can be manufactured simply an economically, whose surface has a low affinity for the components of raw gases before and after scrubbing, and which has a high long-term stability even under alternating stress by cleaning jets.